Cranio-Vertebral Junction -- Craniometry

Dr Chandramohan. U

CV JUNCTION

Parts of CV Junction include:-

The Occiput

First Cervical Vertebra (Atlas)

Second Cervical Vertebra (Axis)

Their articulations and

Connecting ligaments

“The C-V junction is a transition site between mobile cranium and relatively rigid spinal column.

It is also the site of the medullo spinal junction”.

Anatomy of the CV junction

ATLANTO-AXIAL JOINT:

Most active joint in the body, moving approximately 600 times per hour.

Normal range of cervical motion is 900 on each side, range of rotation of atlas on axis being 25-530

Rotation of >560 on one side or a R-L diff >80

implies hyper mobility

Rotation of <280 implies hypo mobility

CV Junction

Anatomy of the CV junction

Occipital condyles

Atlantoaxial joint

Tectorial Membrane

Lateral mass of atlas

Transverse lig

Cruciate Ligament vertical band

Apical Lig

Alar Lig

Plain radiographs (standard FFD)

Lateral

Open mouth

Dynamic Flexion & Extension (to r/o atlantoaxialsubluxation / occipitalization of atlas)

Tomograms –AP and Lateral

Vertebral angiogram

may be necessary in select cases, especially BI

X-ray

X-ray

X-ray

CRANIOMETRY:

Craniometry of the CVJ uses a series of lines, planes & angles

to define the normal anatomic relationships of the CVJ.

These measurements can be taken on plain X rays, 3D CT or

on MRI.

Lines and Angles

The important lines are

Chamberlain’s line

Wackenheim’s clivus canal line

Mc Gregor’s line (basal line)

Mc rae’s line ( foramen magnum line)

Lines and Angles

The important angles are

Basal angle

Bull’s angle

Height index of Klaus

Chamberlain’s line

Synonym Definition Chamberlain's Joins posterior(Palato-occipital Line) tip of hard palate to posterior tip of

Foramen Magnum (opisthion)Tip of dens below this line ±3 mm >7mm or >1/2 of odontoid def basilar Invagination

Mc Gregor’s line

Synonym Definition McGregor’s Line Line drawn from posterior

tip of Hard palate to lowest part of Occiput

Odontoid tip >4.5mm above = Basilar InvaginationShould be used when lowest part of occipital bone is not Foramen Magnum.

Wackenheim’s Line

Synonym Definition Wackenheim's Line drawn along (Clivus canal) line clivus into cervical spinal

canalOdontoid is ventral and tangential to this line

McRae’s Line

Synonym Definition McRae's (Foramen Joins anterior and

Magnum) line posterior edges ofForamen magnum

* Tip of odontoid is below this line.

** When sagittal diameter of canal <20mm, neurological symptoms occur – Foramen Magnum Stenosis

FISHGOLD’S DIGASTRIC LINE(Biventer line)- measured on frontal projectionConnects the digastric grooves ( fossae for digastric

muscles on undersurface of skull just medial to mastoid process)

Line is normally 10mm (+/-4mm) above the atlanto-occipital junction.

Upper limit of position for the odontoid tip

FISHGOLD’S BIMASTOID LINEOdontoid process should be less than 10 mm above this

line

The Boogard’s line

N

O

NAME & SYNONYMS OF

LINES

DEFINITION NORMAL MEASUREMENT IMPLICATIONS

Boogard ‘s Line Nasion to Opisthion Basion should lie below this

line

Altered in basilar impression

Boogard’s angle

NAME & SYNONYMS OF LINES DEFINITION NORMAL MEASUREMENT IMPLICATIONS

Boogard ‘s Angle Angle intersected by

1st line between Dorsum sellae

to Basion &

Mc Rae’s line.

119-1350

Average - 1220

> 1350

Basillar impression

Tuberculum sellaTuberculum sella

B o

N

s

C

Welcher’s Basal Angle

Synonym Definition

BASAL ANGLE Angle between two lines

drawn from

Nasion to tuberculum sella

Tuberculum sellae to the basion along plane of the clivus

Normal – 1240 - 142

> 1450 = platybasia

< 1300 is seen in achondroplasia

BULL’S ANGLE

Line representing prolongation of hard palate and line joining the midpoints of the ant & post arches of C1.

Normal : <100

Basilar invagination - >130

HEIGHT INDEX OF KLAUS

Distance between tip of dens and tuberculum cruciate

line( line drawn from tuberculum sella to internal

occipital protruberence)

Nl- 40-41mm

In basilar invagination-

<30 mm

CRANIO-VERTEBRAL ANGLE

ax

C

NAME & SYNONYMS OF

LINES

DEFINITION NORMAL MEASUREMENT IMPLICATIONS

Cranio vertebral angle Between clivus line and

post axial line

Flexion – 1500

Extension - 1800

<1500 Platybasia

cord compression

Basilar impression

NAME &

SYNONYMS OF

LINES

DEFINITION NORMAL

MEASUREMENT

IMPLICATIONS

Schmidt – Fischer

Angle

Angle of axis of

Atlanto-Occipital joint

125 +/- 2 degrees Angle is wider in

condylar hypoplasia

Schmidt – Fischer Angle

(ATLANTO-OCCIPITAL JT AXIS ANGLE)

O

C2

AA JT

AO JT

C1 C1

Platybasia – refers only to an abnormally obtuse basal angle, may

be asymptomatic, and is not a measure of basilar invagination.

Ranawat method

Ranawat method Line joining center of the

anterior arch of C1 to post ring

& another line along the axis

of the odontoid from the centre

of the pedicle of C2 to 1st line

Normal distance between C-1

and C-2 in

Men averages 17 mm (±2 mm SD)

Women, 15 mm

(± 2 mm SD).

A decrease in this distance

indicates cephalad migration of

C-2.

C2

C1

C2

C1

C2

C1

PEDICLE

•BASILAR

INVAGINATION

•Floor of the skull is indented by the upper

cervical spine, & hence the tip of odontoid

is more cephalad protruding into the FM.

•Two types of basilar invagination:

primary invagination, and secondary

•Primary invagination can be associated

with occipito atlantal fusion, hypoplasia of

the atlas, a bifid posterior arch of the atlas,

odontoid anomalies.

•BI is associated with high incidence of

vertebral artery anomalies.

BASILAR IMPRESSION

(SECONDARY BASILAR

INVAGINATION

•Basilar impression refers to secondary or

acquired forms of BI

• Due to softening of the bone

• Seen in conditions such as rickets,

hyperparathyroidism, osteogenesis

imperfecta, Paget disease, neurofibromatosis,

skeletal dysplasias, and RA & infection

producing bone destruction.

Anterior Atlanto-Dental Interval (AADI) :

AAS is present when it is >3mm in adults & >5mm in children

Measured from posteroinferior margin of ant arch of C1 to the ant surface of odontoid

AADI 3-6 mm trans lig. damage

AADI >6mm alar lig. damage also

AADI >9mm surgical stabilization

ATLANTO-AXIAL SUBLUXATION (AAS) : anterior

type

Posterior Atlanto-Dental

Interval (PADI) :

** Distance b/w posterior

surface of odontoid & anterior margin of post ring of C1

Considered better method as it directly measures the spinal canal

Normal : 17-29 mm at C1

PADI <14mm : predicts cord compression

Pseudosubluxation

In children, C2-3 space & sometimes C3-4 space have normal physiologic displacement

Line drawn from ant. aspect of spinous process of C1-3 should not be >1mm far from any spines

RISK FACTORS FOR CORD COMPRESSION IN AAS

AADI > 9 mm

PADI < 14 mm

Basilar Invagination, especially if associated with AAS of any degree

Sub axial canal diameter < 14 mm

Cerebellar tonsils

medulla

Vertebral artery

basion

Medulla oblongata

basion

Anterior arch of atlas

Atlas (anterior arch)

Transverse lig. atlasDens of axis

Medulla oblongata

Vertebral artery

Atlas, posterior arch

Atlas, lateral mass

Transverse ligament of atlas

Transverse process and foramen transversarium

Anterior longitudinal ligament

Apical ligament of dens

Tectorial membrane

Transverse ligament of atlas

Anterior arch of atlas

Dens of axis (C2)

Clivus

Anterior atlanto-occipital membrane

Atlas (lateral mass)

Axis

Int carotid artery